The present invention relates to a contact-making arrangement and to a preassembled contact-making unit of a contact-making arrangement such as this, which has a nut and a holding unit.
The present invention also relates to a nut for a contact-making arrangement such as this, and to a method for forming an electrical contact between at least one connecting part such as a cable lug and a contact substrate such as a workpiece.
In general, the present invention relates to the field of so-called earth contacts, such as those which are used widely in particular in motor vehicle engineering. In order to make a robust earth contact, a bolt or a nut is welded to a metal sheet of the vehicle bodywork, so that the bolt or the nut is electrically conductively connected to the metal sheet. A connecting part such as a cable lug is then electrically connected to the bolt or to the nut, by screwing a nut onto the bolt or by screwing a screw into the nut.
One general problem in this case is that a painting process is carried out between the bolt (nut) being welded on and the connecting part (cable lug) being fixed. In order to keep the contact surfaces free of paint in order to make an electrical connection, it is known for these contact sections to be covered. The covering parts which are used for this purpose are in this case thrown away before the connecting part is fixed. It is known from the document EP 0 641 944 A1 for a nut to be used as the covering part, which is also then used once again to attach the connecting part. There is therefore no need to throw a part away. However, the overall assembly process is somewhat more complex.
It is known from German patent application 10 2006 056065.5 for a bolt with an axial blind hole to be welded to a metal sheet. In this case, the bolt with the blind hole has a first threaded section in the blind hole, which first threaded section is covered by a covering part and in particular a plug, which is relatively short and is inserted into the blind hold from above. A cable lug is pushed onto a screw with a second threaded section, and the screw is screwed into the blind hole. During this process, the plug is forced downwards to the base of the blind hole. At least one threaded section of the two threaded sections may be in the form of a self-tapping threaded section. In consequence, an electrical contact is made in this way between the cable lug and the lower face of a head of the screw, and via the self-tapping threaded engagement between the screw and the bolt with the blind hole, and in consequence with the metal sheet to which the bolt with the blind hole is welded.
In this case, it is also known from the cited German patent application for at least one cable lug to be inserted into a holding unit in the radial direction, and for a screw then to be inserted into the holding unit. In this case, the shank of the screw passes through the hole in the cable lug, and latching means being engaged behind the head of the screw. This results in a preassembled attachment arrangement which has the holding part, the screw and at least one cable lug that has been threaded onto the screw. Since the screw passes through the hole in the cable lug, this prevents the cable lug from being pulled out of the holding unit radially. In addition, further latching means may be provided in order to prevent the screw from falling out of the holding part. In one particular embodiment, in the case of a holding part, apart from radial holes for cable lugs to be inserted into it from the side, provision is also made for a further cable lug to be forced into the holding device from underneath in the axial direction onto the preassembled attachment arrangement, comprising the holding part, the screw and the at least one cable lug. This particular embodiment can be used as follows. The preassembled attachment arrangement described above can be fitted in advance to a cable harness. In this case, for example, one or more cable lugs can be inserted into the holding unit from the side thereof and the screw can then be passed through in order to hold both the screw and the cable lugs captive on the holding unit. During fitting of the cable harness, one or more further cable lugs can then be inserted into the holding part from underneath, that is to say in the longitudinal direction, retrospectively in situ, and can be pushed onto the screw before the screw is screwed into a bolt with a blind hole as described above (earth bolt).
German patent application 10 2007 057 082.3 discloses a preassembled contact-making unit having a screw which has a head and a shank, and having a holding unit, with the holding unit having a connecting part holding section into which at least one connecting part can be inserted, and has a screw holding section into which the screw is inserted in the longitudinal direction, such that the screw is held captive in the longitudinal direction, but can rotate, and in which case a connecting part which is inserted into the connecting part holding section can make electrical contact with the inserted screw, with a radially projecting contact section being formed on the head and with the screw holding section having a shoulder section by means of which the contact section is supported axially on the holding unit.